Streptococcus pyogenes, more commonly known as group A β-hemolytic Streptococcus, is the etiologic agent of a number of infections in humans including acute pharyngitis, sinusitis, lymphadenitis, pyoderma, endocarditis, meningitis, septicemia, tonsillitis, impetigo, and upper respiratory tract infections. Streptococcus pyogenes infections are of particular concern because serious complications such as glomerulonephritis, rheumatic fever and scarlet fever may result if left untreated. Group A β-hemolytic streptococci are universally susceptible to penicillin G, a fact that makes antimicrobial susceptibility testing for this organism unnecessary unless the patient is allergic to penicillin.
Over ninety percent of all streptococcal infections are caused by Streptococcus pyogenes. Asymptomatic carriers colonized in the nasopharynx, skin, vagina or rectum are thought to transmit this organism through close person-to-person contact. Contaminated food may also be a source of transmission and infections in humans.
Presumptive identification of Streptococcus pyogenes was traditionally based upon physiological and biochemical traits. These include colony morphology, β-hemolytic activity on sheep blood agar, gram strain, susceptibility to bacitracin, and the ability to hydrolyze L-pyrrolidonyl-β-naphthylamide (PYR). Commercial antibody tests such as latex agglutination targeted the Streptococcus group A antigen. Occasionally, these tests were shown to react positively with some strains of Streptococcus anginosus containing the group A antigen. In addition, these tests occasionally required repeat testing due to equivocal results. Serological grouping was the method of choice for definitive identification of Streptococcus pyogenes. Lancefield serological grouping is determined from group-specific carbohydrate antigen extracted from cell walls and group-specific antisera. This method can be time-consuming and costly, therefore most laboratories relied on the traditional physiological and biochemical methods.
More recently, DNA probe assays have aided in the diagnosis of Group A Streptococcal pharyngitis from throat swabs. The DNA probe assays use nucleic acid hybridization for the qualitative detection of Group A Streptococcal DNA and RNA. Such tests offer a non-subjective, accurate and rapid identification method for definitively identifying Streptococcus pyogenes from throat swabs. Identification is based upon the detection of specific ribosomal RNA sequences that are unique to Streptococcus pyogenes. Such tests identify Streptococcus pyogenes organisms from throat swabs within 60 minutes of sample preparation.
The present invention improves upon the DNA probe assays by: increasing the sensitivity, precision and specific detection of Group A streptococci; providing for the ability of qualitative and quantitative measurements; and, increasing the speed of detection of low target copy levels due to the combination of amplification and detection in real-time.